Josip Vrandecic -Mes Posted October 22, 2014 Share Posted October 22, 2014 @ Colin , It's understandable that they are staring, because they are envious over your beautiful balcony view, and perhaps notice and your good thinking...sir... (abt depron.....lol) ... Rgds Jo Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted October 22, 2014 Author Share Posted October 22, 2014 Thanks again Jo! Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted October 22, 2014 Author Share Posted October 22, 2014 Still thinking about my Chipmunk. (Sigh). Bearing in mind Danny's thoughtful observation about the need to consider vibration with an I/C motor, (particularly a four-stroke), it had occurred to me that using the Depron, particularly on the sheeted areas, is likely to reduce airframe vibration frequencies compared to wood. It will probably have a significant dampening effect on vibrations transmitted through the structure. We will see. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 8, 2014 Author Share Posted November 8, 2014 Back home, look at the weather! First time back in the shed this afternoon for a couple of hours. First job was to create the elevator shroud by sticking back on the 3mm strips of Depron I shouldn't have cut off in the first place. Then finished off the elevators, sanding the Depron tips and gluing the 1/32" cap strips in exactly the same fashion as used on the rudder. Put a coat of Ezekote on tailplane and elevators in readiness for covering. While that was drying I sorted out the bits to start building the starboard wing panel. I'd toyed with the idea of doing the fuselage next but decided to go with the flow Instead. I'll work out the details for the wash-out next. I don't think I'll catch up with anyone because of limited shed time, but we'll see how it goes. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted November 8, 2014 Share Posted November 8, 2014 You're bench is a disgrace just like mine I think it's best to do the wing first Colin get it out the way, fuzz is much easier. John Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 8, 2014 Author Share Posted November 8, 2014 We should have a competition John, I bet mine's worse than yours! Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted November 8, 2014 Share Posted November 8, 2014 It is, here you go first prize John Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 9, 2014 Author Share Posted November 9, 2014 Thanks John, I'll treasure that. What's more, you haven't seen the worst end! As for what's underneath the bench, don't go there! Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 9, 2014 Author Share Posted November 9, 2014 I've just had a look at the plan to measure what the lift needs to be on rib 18 (in front of the aileron) to get 2 degrees of wash-out. I make it 7mm. ZK BAP said that the Airsail plan shows 6.5mm so based on the margin of error within my squinty eye-ball I reckon that'll do. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 11, 2014 Author Share Posted November 11, 2014 I've got work commitments every day this week, so it's limiting my build time. However I managed to do a bit tonight, concentrating on getting the clearance for the elevators in the shrouds right. Put on another coat of Ezekote, everything is ready now for covering exactly as per the rudder. Will start on the wing tomorrow night, I've got my head around it now. To compensate for the reduction of one degree in the wing incidence caused by the two degrees of wash-out, I will increase the wing incidence at the wing root by one degree rather than compensate at the tailplane. That way I won't need to make any change to the engine thrust line. When I decided to use the composite approach for the tail surfaces I was prepared to have to try more than once, but what I've got at the first attempt I'm happy with, so I'm going to use them as they are. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted November 11, 2014 Share Posted November 11, 2014 That's a good start then Colin John Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 12, 2014 Author Share Posted November 12, 2014 This is how I've decided to set the 2 degrees wash-out. Originally I'd thought about using tabs on the ribs, but instead I've made a "toast rack" out of 3mm Liteply. To get the 2 degrees at the tip I found that rib 18 needed a 7mm uplift. At 0 degrees there was already a 3mm uplift, so it needs 10 altogether. Rib 1 has 6mm uplift at 0 degrees, so a straight line drawn from rib 1 to rib 18 starting at 6mm and going up to 10 gives the correct amount of twist along the trailing edge. Marking at each rib position in between gives the correct lift for each. This shows the ribs slotted in dry. It will probably be the weekend before I can do any more, sadly. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted November 12, 2014 Share Posted November 12, 2014 Ah very clever, will you have to ease the spar slots a little to stop it taking the twist back out ? then the l/e and t/e will hold it. It looks quite a lot Colin..that's the camera exaggerating it ? John Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 12, 2014 Author Share Posted November 12, 2014 If everything's glued up while the ribs are held in position it should lock it in, but I'll sort it out as I go along John. The camera angle does exaggerate the twist, but it's surprising just how much even 2 degrees makes along the length of the wing. I think I'm comfortable with it. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted November 12, 2014 Share Posted November 12, 2014 It works for the real thing so it can't be wrong Colin John Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 12, 2014 Author Share Posted November 12, 2014 I think so John, not that I think there's anything wrong with Dennis's design, it's just something I like to do. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 13, 2014 Share Posted November 13, 2014 Colin An excellent build so far. Just an observation about Depron and vibration. Whilst I would expect Depron to damp out vibration better than wood I am not sure it is entirely to your advantage as Depron is also much more flexible thus likely to make any vibration issue rather worse.. To counter its flexibility might require some form of additional skin (like the brown paper that Tony is using on his Depron TSR2) but the extra weight does erode into the weight advantage of using Depron although it is still a great deal cheaper. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 13, 2014 Author Share Posted November 13, 2014 Simon, thank you, your interest is much appreciated. I think that having a four-stroke up front focuses your mind on vibration issues. Most of the structure will be wood as designed, apart from what you have seen so far in the tail feathers, the bulk of the Depron will be in the wing and fuselage sheeting/planking. I've no problem with uncoated Depron for an electric application, but for this I share your reservations. Following what I learned with the Barnstormer, all of the exposed Depron will be coated with glass cloth and Exekote/PolyC. I have found this to be at least as tough as balsa, if not more so. As you say, a lot of the weight saving is lost and the result will be measured in ozs saved rather than lbs, but it is worth having and what is more it is a lot cheaper and certainly not worse, it might even be better. If this works out, I intend to use the same approach for skinning the wooden airframe of the 317. I remain on the learning curve, but stay optimistic. Quote Link to comment Share on other sites More sharing options...
Terry Walters Posted November 13, 2014 Share Posted November 13, 2014 Colin - very interesting - keep it coming. I'll have to have a go with mixing in Depron at some point in the future too. Terry Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 13, 2014 Author Share Posted November 13, 2014 Will do Terry. So far, so good. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 14, 2014 Author Share Posted November 14, 2014 I'll do a bit more this evening, starting on the starboard wing. I've looked carefully at it and using the "toast rack" to hold the wash-out as I assemble it makes no change to the build, all it adds is the 15 minutes or so to make it. One thing I will change is the treatment of the leading edge and top sheeting. The plan shows on both wing and tailplane the sheeting wrapped over the leading edge. I've no problem with that normally and have done it with the Depron on the tailplane, lapping it over the leading edge and then sanding, no problem. However for the wing, it looks to me as though the leading edge needs to be shaped before the sheeting can be attached. To me that needs lifting it off the building board after the l/e is glued on, then sanding it to shape. I don't want to do that, because I want to glue the panel up as far as I can and attach the top sheeting before I take it off the board, to make it rigid and lock in the wash-out. The wing looks to me as if without the sheeting it is rather flexible, with or without wash-out. Therefore I will make the l/e 4mm oversize to allow a 2mm overlap top and bottom. That will allow me to butt the sheeting up to the l/e while still on the board. When all is set, I will lift it off and shape the l/e and blend the sheeting in, all in one go. I'll find out how it all works. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted November 14, 2014 Share Posted November 14, 2014 Sounds like a sensible approach Colin John Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 14, 2014 Author Share Posted November 14, 2014 I hope so John. Just come in after preparing all the bits, leading edges, B1 etc. etc. Ready to start gluing together now. I'm taking note of your approach to the undercarriage. Originally I was going to break the wing down into three pieces, but I've decided to stick with the plan for the centre section, it will do. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 18, 2014 Author Share Posted November 18, 2014 A fair bit of codging to get this far and slower than I expected. However making progress. The toast rack idea for setting the wash-out has worked well. I don't want anyone to think I'm suggesting that the model needs it desperately, clearly it's a good flyer without it. However, it's my preference and is a scale feature, the twist on the wing is visible on the full-size and I don't see any reason not to do it. It's created thinking time rather than build-time! Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted November 19, 2014 Share Posted November 19, 2014 Yes you can see it, it looks to have gone together nicely Colin John Quote Link to comment Share on other sites More sharing options...
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